The disclosure relates to turbofan engines. More particularly, the disclosure relates to erosion coatings.
FIG. 1 shows a gas turbine engine 20 having an engine case 22 surrounding a centerline or central longitudinal axis 500. An exemplary gas turbine engine is a turbofan engine having a fan section 24 including a fan 26 within a fan case 28 held spaced apart from the engine case by a circumferential array of fan struts 29. The exemplary engine includes an inlet 30 at an upstream end of the fan case receiving an inlet flow along an inlet flowpath 520. The fan 26 has one or more stages 32 of fan blades. Downstream of the fan blades, the flowpath 520 splits into an inboard portion 522 being a core flowpath and passing through a core of the engine and an outboard portion 524 being a bypass flowpath exiting an outlet 34 of the fan case.
The core flowpath 522 proceeds downstream to an engine outlet 36 through one or more compressor sections, a combustor, and one or more turbine sections. The exemplary engine has two axial compressor sections and two axial turbine sections, although other configurations are equally applicable. From upstream to downstream there is a low pressure compressor section (LPC) 40, a high pressure compressor section (HPC) 42, a combustor section 44, a high pressure turbine section (HPT) 46, and a low pressure turbine section (LPT) 48. Each of the LPC, HPC, HPT, and LPT comprises one or more stages of blades which may be interspersed with one or more stages of stator vanes.
In the exemplary engine, the blade stages of the LPC and LPT are part of a low pressure spool mounted for rotation about the axis 500. The exemplary low pressure spool includes a shaft (low pressure shaft) 50 which couples the blade stages of the LPT to those of the LPC and allows the LPT to drive rotation of the LPC. In the exemplary engine, the shaft 50 also drives the fan. In the exemplary implementation, the fan is driven via a transmission (not shown, e.g., a fan gear drive system such as an epicyclic transmission) to allow the fan to rotate at a lower speed than the low pressure shaft.
The exemplary engine further includes a high pressure shaft 52 mounted for rotation about the axis 500 and coupling the blade stages of the HPT to those of the HPC to allow the HPT to drive rotation of the HPC. In the combustor 44, fuel is introduced to compressed air from the HPC and combusted to produce a high pressure gas which, in turn, is expanded in the turbine sections to extract energy and drive rotation of the respective turbine sections and their associated compressor sections (to provide the compressed air to the combustor) and fan.
FIG. 2 shows an assembly of a fan exit case (including the exit guide vanes 29 and a circumscribing hoop structure 100) and a compressor intermediate case 102 (wherein a circumferential array of struts 104 structurally join an inner wall 106 of the core flowpath to an outer wall 108). The outer wall bears radial struts 110 that mate with inboard flanges 112 of the fan exit guide vanes 29 proximate the core nacelle (not shown) which defines the inboard boundary of the bypass flowpath.
The vanes 29 and the inboard surface of the fan case (e.g., along the hoop structure 100) bear an erosion coating. Similarly, a military style turbofan engine 200 (FIG. 3) may have an inlet case 202 and inlet vanes 204 (e.g., variable vanes) ahead of the fan 206 and which may bear an erosion coating. Exemplary erosion coatings are silicone. These coatings are subject to damage.